Add support for exemplarTraceIdDestinations in Prometheus data source

[johanderss]

Is your feature request related to a problem? Please describe.
The Prometheus data source has support for exemplars but the fields need to be whitelisted in Grafana Operator.

Describe the solution you'd like
Add support for the following type in jsonData:

export type ExemplarTraceIdDestination = {
  name: string;
  url?: string;
  urlDisplayLabel?: string;
  datasourceUid?: string;
};

Example data source can be found here Provision the Prometheus data source